Shell Mathematical Expression

By default, operations in Shell programs are string operations, and unexpected answers may be obtained when you want to run mathematical operators:

Var = 1
Var = $ var + 1
Echo $ VaR

Output:
1 + 1

From this example, we can see that the shell string connection operation requires spaces. In Shell, let can be used to indicate the following arithmetic expressions:

Var = 1
Let "Var + = 1"
Echo $ VaR

Output:
2

Here, Let can be replaced by (), just as it is used in many cycles:

Var = 1
(VAR ++ ))
Echo $ VaR

Output:
2

There is also a way to write:

Var = 1
Var = $ [$ var + 1]
Echo $ VaR

Output:
2

When using expr, note that the symbol is not a single quotation mark, but the key on the left of "1:

Var = 1
Var = 'expr $ var + 1'
Echo $ VaR

Output:
2

The above methods can only process integer operations. The following method can process floating point numbers:

Var = 1
Var = 'echo "$ Var * 2.0" | BC'
Echo $ VaR

Output:
2.0

The 'symbol above is the same as the one on the left, while BC is a calculator on Linux. It supports all operations except bit operations. Another method that supports floating-point operations is awk:

Var = 1
Var = 'echo "$ var 1" | awk '{printf ("% G", $1 + $2 )}''
Echo $ VaR

Output:
2

The above are some of the methods we have just seen. I will try again later.

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